Laser apparatus sold commercially typically includes a plurality of optical elements. Such optical elements include resonator mirrors, beam-steering mirrors, and lenses for focusing or collimating a beam. Most such elements require precise alignment during manufacture of the device, but it is desirable that after this manufacturing alignment is complete the elements stay essentially permanently aligned.
Typical methods for “permanent” alignment of optical elements involve attaching an optical element to a mount or pedestal using a hard-curable adhesive, such as an epoxy, or using a solder bond. In such methods, the optical element is on the mount while the adhesive is soft and uncured or while the solder is in a thermally softened, at least partially molten, condition. After alignment is complete, the adhesive is allowed to cure, or the solder is allowed to solidify. Solder-bonding is preferred as adhesives can create problems traceable to out-gassing products of the adhesives.
One effective solder-bonding method for an optical element is described in U.S. Pat. No. 5,930,600, assigned to the assignee of the present invention. In this method, a positive thermal coefficient thermistor (PCT) is supplied with a constant current to heat the PCT and soften the solder used for bonding. The PCT is bonded to a pedestal attachable to a base-plate on which the optical element is to be mounted. The optical element is bonded on a pedestal attached to the PCT and which can be aligned when the solder is soft. Once the alignment is complete, current to the PCT is cut off and the solder solidifies, maintaining the optical-element in the optical alignment.
While this method is effective and has been verified as reliable through several years of commercial use, the method nevertheless has certain shortcomings. One shortcoming is simply the cost of the PCT, which remains part of the optical element mount once the alignment is completed, yet has no further useful function. Another shortcoming is that two solder bonds are required in the mount. Yet another shortcoming is that careful selection of metal parts is required such that there is an acceptable coefficient of thermal expansion (CTE) match between the mount and the optical element, and between the mount and the base-plate. There is need for a an optical element mount that allows a mounting method similar in principle to that of the '600 patent while at least mitigating, if not altogether eliminating, the above described shortcomings thereof.